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My iPhone was using > 2GB a month in data, and 99% of it was due to DNS. Consistently I was chewing up 50-100MB in data per day. I would go to Cellular->System Services->DNS and see very little usage elsewhere, but high GB usage for DNS.

What could possibly cause this? A DNS query is an ipv4 packet or two...

All the other data usage clearly correlated to my actual usage but I could not understand DNS.

This is on an iPhone 8+ that is always updated to the latest iOS within a few days.

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Turns out my ad blocker (1Blocker) was the cause. Once I disabled it, DNS usage flatlined to near zero. I was chewing up 50-100MB a day in DNS and now it's been a single MB in a week.

Strangely, I have Safari blocked from using cellular. I often tether another phone's hot spot for use, but that should burn data on that phone and not this one. Still, 1Blocker burned a ton of data use on this phone. I don't know if that means it's poorly designed or it was doing something shifty under the covers.

  • That's interesting, I've been using 1Blocker on my iPhone X since the X came out and I've never noticed such high DNS data usage. My iPhone shows 13.3 MB of data for the last 3 weeks (last reset). I'll keep an eye on it and see if I get similar results to you. – fsb Jun 12 '18 at 19:52

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